Electromechanical transducer for watches

ABSTRACT

A stepping mechanism used in a watch includes an elongated air core moving coil which is rotatably mounted between magnetic poles with the longitudinal axis parallel to the pole faces. Current pulses through fixed coil springs at the ends rotate the moving coil in one direction with the springs causing return to the steady state position. The moving coil rotates a pawl carrier on an axial shaft which causes a pawl to engage a tooth of a ratchet on a crown gear. A second spring loaded fixed pawl engages another tooth to prevent movement in the reverse direction. Limit pins provide an angular rotation to engage one tooth at a time. The crown gear axis is perpendicular and aligned with the moving coil axis.

United States Ptet [191 1 9 SChliCill @CL 29, 1974 ELECTROMECHANICALTRANSDUCER Primary ExaminerEdith Simmons .lackmon FOR WATCHES Inventor:Walter Schlicht, Freiburg, Germany lnternational Telephone and TelegraphCorporation, Nutley, NJ.

Apr. 9, 1973 Assignee:

Filed:

Appl. No.:

nepr a i n t n ty D ta Apr. 8, 1972 Germany P 22 16 992 Attorney, Agent,or FirmJoht-1 T. OHalloran; Menotti J. Lombardi, Jr.

[5 7] ABSTRACT A stepping mechanism used in a watch includes anelongated air core moving coil which is rotatably mounted betweenmagnetic poles with the longitudinal axis parallel to the pole faces.Current pulses through fixed coil springs at the ends rotate the movingcoil in one direction with the springs causing return to the steadystate position. The moving coil rotates a pawl carrier on an axial shaftwhich causes a pawl to engage a tooth of a ratchet on a crown gear. Asecond spring loaded fixed pawl engages another tooth to preventmovement in the reverse direction. Limit pins provide an angularrotation to engage one tooth at a time. The crown gear axis isperpendicular and aligned with the moving coil axis.

9 Claims, 6 Drawing Figures PATENTEDum 29 1914 3;84.4'.104 SHEEY NF 3Fig. 2a

PATENTEDnm 29 I974 SHEEI 30F 3 ELECTROMECIIANICAL TRANSDUCER FOR WATCHESBACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention concerns a novel stepping mechanism for watches andparticularly to a more reliable efficient electromechanical transducerwhich uses an air core coil mounted on springs to drive a pawl andratchet mechanism.

2. Description of the Prior Art As a result of the development ofmonolithically integrated binary frequency dividers forcrystal-controlled watches, it is now possible for the watchmanufacturer to depart from the balance-wheel principle and to usesimple stepping mechanisms for driving the hands of clocks and watches.Since the accuracy of such clocks and watches is exclusively dependentupon the stability of the crystal resonator frequency, such steppingmechanisms merely have to convert the low-frequency output pulses of thefrequency dividers into a mechanical movement.

As a rule, these stepping mechanisms operate on the electrodynamicprinciple wherein a moving coil arranged within a permanent magneticfield on reset springs is angularly deflected against the spring actionas soon as a current is permitted to flow in the coil, with the coilreturning to normal upon disconnection of the current.

In a known previous arrangement, the moving coil is wound on a core andis excited into mechanical resonance for stepping along a toothedratchet wheel by pawl mechanisms.

In this conventional arrangement the core-wound moving coil has a lengthwhich is substantially greater than the diameter of the coil, thusachieving a small moment of inertia. Owing to the fact, however, thatthe mechanical resonant frequency of the moving coil system must betuned to the reduced frequency of the output pulses of the frequencydivider, the dimensions of the known type of moving coil must be heldvery accurately, and are therefore particularly critical. The resonanceprinciple also makes it necessary for the moving coil to be deflected byat least 180 In addition, this requires a moving coil oscillatingfrequency in the order of some Hertz, so that a mechanical gearreduction is necessary between the ratchet wheel and the crown gear.

Although this arrangement is supposed to be relatively insensitive toexternal shock and impact, it is possible that strong arm movements willaffect the drive of the ratchet wheel to cause irregular steppingoperation. In addition, very narrow tolerances must be adhered to forboth the moving coil and the spiral springs, since inaccuracies in theweight and the dimensions of the coil and springs have a great influenceupon the resonant frequency of the moving coil. Finally, substantialenergy is required to effect the continuous step-by-step v accelerationof the ratchet wheel.

SUMMARY OF THE INVENTION It is therefore the object of the presentinvention to avoid the disadvantages of the prior arrangements, and toprovide a novel electromechanical transducer for watches which does notrequire specific tolerances for the moving coil and which is insensitiveto shock and spin movements and in which irregularities due to suddenacceleration of the ratchet wheel are negligible. According to thepresent invention, this is accomplished by a moving coil having anair-core without an iron core. At one end of the coil axis, there is adriving pawl which engages one of the teeth of the crown gear having aknown type of surface toothing. The shaft of the gear verticallyintersects the coil axis from which the pawl extends. A magnetic yokesupports another stationary pawl engaging another one of the teeth ofthe crown gear. The pawls and teeth of the crown gear are designed sothat the gear is stepped by one tooth during each resetting of themoving coil. The device is used in quartz watches for stepping the crowngear by rotation of the moving coil which is traversed by a currentpulse. The coil oscillates on reset springs within the airgap of apermanent magnet which includes the magnetic yoke. The moving coil has adiameter which is relatively small compared to its length.

An example of a particular embodiment of the present invention will nowbe explained in greater detail with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows a perspective view of anelectromechanical transducer according to the present invention,

FIG. 2 shows a side view in partial cross-section of theelectromechanical transducer of FIG. 1,

FIG. 2a shows an enlarged view of a portion of the device of FIG. 2, and

FIGS. 3a, b and 6 show top, front and side views of a tool for use inmanufacturing the coil of the electromechanical transducer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the novelelectromechanical transducer of the present invention with all of theelements mounted on a base plate 4 which may be either of insulatingmaterial or metal. On the base plate are two magnet poles I which,together with the magnetic yoke 6, constitute a permanent magnet systemfor producing a radial magnetic field within the airgap as formed by themagnet poles N, S.

The moving coil 2 is arranged with its longitudinal axis in the airgapbetween the magnet poles N, S, so that the axis will extend parallel inrelation to the plane surface of the base plate 4. The lower end ismounted on a shaft I4 supported in a journal bearing 5 which, dependingupon the required mechanical quality of the transducer, may be providedwith a jewel. A second journal bearing for the upper end of coil 2 andshaft 14 is arranged in the upper transverse portion of magnetic yoke 6.

The moving coil 2 is connected to a pair of spiral springs, one at eachof the upper and lower ends, through which the current pulse requiredfor deflecting the coil is applied. The inner ends of the spiral springs3 are secured at opposite ends of the shaft 14 and the outer ends aremounted on a holder 16 made of insulating material and fixed to the baseplate 4 by means of a clamp 15 which also is of an insulating material.

Mounted on the base plate above the transverse portion of the magneticyoke 6 is a bearing bridge 9 for the crown gear 8 which has a shaft 17extending vertically in relation to the base plate. The crown gear isprovided with teeth around the outer surface in a known configuration.The shaft 17 of the crown gear 8 is arranged to vertically intersect aline extending from one end of coil axis 14.

A pawl carrier 7 is mounted centrally on the end of the coil axis shaft14 extending towardcrown gear 8. The pawl is secured at one end ofcarrier 7. Mounted on base plate 4 below the two ends of the carrier aretwo limiting stop pins 13 which restrict rotary movement of the movingcoil 14 to about 20 as the pawl carrier 7 meets the stop pins. Anotherratchet pawl 11 is mounted'on the right side of magnetic yoke 6 andsecured by a clamping member 12.

Both the pawl 10 and the teeth of the crown gear 8 are so designed thatthe crown gear is stepped by a single tooth during each resetting of themoving coil. For thispurpose a pawl stop 18 is provided, with the pawl10 engaging the end surface thereof. The pawl stop 18 is mounted on theleft side of magnetic yoke 6 and secured by clamping member 19.

The moving coil Zwhich is wound without a core, is retained in'theindicated normal position by the spiral springs 3. The dashed line inFIG. 2 shows the position ofthe pawl carrier 7 in the condition afterthe moving coil has been deflected by a current pulse. Due to thedeflection of the moving coil, the pawl carrier 7 is deflected untilmeeting the limiting stop pin shown on the right side in FIG. 2, so thatthe pawl 10 will engage the successive tooth of the crown gear 8 lyingnext to the original tooth. Upon termination of the current flow in themoving coil 2, the latter is returned to the normal position by theaction of the spiral springs, so that pawl 10 engages a tooth and stepscrown gear 8 in the clockwise direction. At the same time the ratchetpawl 11 engages anew tooth.

From theenergy standpoint, this action is equivalent to the oppositeembodiment which steps the gear duri'ngthe initial deflection of thecoil. However, due to the stepping movement being effected while themoving coil is returning to normal, the coil is deflected by a shortcurrent pulse, and thus sufficient time remains for. the stepping actionduring the comparatively long interval between two successive currentpulses. To achieve reliable operation, the duration of the current pulsecan be adjusted so that the pawl carrier 7 reaches the limiting stoppins 13 prior to the termination of the current pulse.

FIG. 2a, on an enlarged scale, shows a further embodiment of theinvention. The pawls 10, 11 which may be in the form of springs 10b,11b, carry jewels 10a, 11a. The jewel 10a of pawl 10 has a wedge-shapeat its end which is in engagement with a tooth of the crown gear 8and-is mounted on spring 10b so that the edges of the jewel 10a will fitagainst both the front and the rear faces of a tooth of the crown gear8. The front face of the tooth is the primary one that meets the pawlduring the stepping operation.

In the normal position of the coil, the end of jewel 10a of pawl 10 alsocontacts a correspondingly shaped end surface of the pawl stop 18, whilethe top surface area of the jewel contacts the rear surface of therespective tooth of the crown gear 8. Both the top and bottom surfacesof jewel'l Oa together form an angle of preferably 15 to 18 while thesurfaces of both the front and the rear face of the teeth are preferablyvertical with respect to each other.

This embodiment of jewel 10a reliably prevents the crown gear from beingstepped in excess of one circular tooth pitch, since the rear face ofthe tooth which is in egagement with the jewel, upon further rotation orany external acceleration, would have to press the jewel vertically inthe downward direction. Such movement, however, is prevented by thejewel meeting the end surface of the pawl stop 18. Turning of the crowngear 8 in the opposite direction is also prevented by the ratchet pawl11, so that the crown gear 8 will remain firmly oriented in its positionafter each stepping opera tion. Preventing the crown gear from beingfurther rotated can also be realized without the aid of a jewel. Forthis purpose, the pawl stop 18 would have to be extended so that in thenormal position of the moving coil 2 the spring of the pawl, will meetthe end surface of the stop.

Since the present electromechanical transducer does not employmechanical resonance as used in the prior art, the moving coil can bemade much more simple, with the dimensions being uncritical as regardsthe stepping reliability. The present device can therefore use acoreless or air core coil. Such a coil can be made easily as shown inFIGS. 3a, b and c.

For this purpose, a U-shaped coil winding tool 21 is used which is madefrom a flexible material with the ends having the capability of beingpressed together. Each end of the U-shaped tool 21 is provided with arecess 20 into which the coil is wound. Upon application of thenecessary number of turns, the individual coil windings are secured inposition with respect to one another either by spraying with, orimmersion into, a lacquer. Upon hardening of the lacquer, the ends ofthe U-shaped tool are pressed together to permit the coil to be removed.

Since the present transducer can be operated with relatively shortcurrent pulses, the moving coil may be wound with substantially lessresistance than a coil used in the mechanical resonance typearrangement. This permits normal sized wire to be used. The currentflowing in the coil is then momentarily larger than in the conventionalarrangement. However, since current flows only for a fraction of asecond, the entire energy consumption of this arrangement is about onequarter less than in the conventional arrangement. This saving of energycan be utilized to operate frequency-divider stages to further reducethe usual frequency of some ten Hertz to a frequency of one Hertz.

What is claimed is: r

1. An electromechanical stepping device comprising a magnetic yokehaving a pair of opposite facing poles, a movable air core coilrotatably supported between said poles on a shaft having a longitudinalaxis between and parallel to the opposite faces of said poles, a pair ofreset springs secured at opposite ends of said shaft and connected tosaid coil to apply current thereto, both said springs being rotatablewith said coil and shaft and returning said coil to a reset position, atoothed gear mounted on a central axis, said gear axis being alignedwith and perpendicular to said coil shaft axis, and a first pawl mountedat one end of said shaft to rotatably engage separate successive teethof said gear upon each return movement of said coil after application ofa current pulse to rotate said coil, said gear being stepped by onetooth during each return movement of said coil.

2. The device of claim 1 including a pawl carrier rotatably mounted atone end of said shaft securing said first pawl thereon, and a pair oflimit stop pins mounted under each end of said carrier to limitrotatable movement of said carrier.

3. The device of claim 2 including a second pawl secured at one side ofsaid yoke to successively engage another one of said teeth of said geareach time said first pawl engages a tooth.

4. The device of claim 3 including a pawl stop secured at the other sideof said yoke to limit movement of said first pawl.

5. The device of claim 4 wherein said first and second pawls are mountedat the ends of springs.

6. The device of claim 5 including a pair of jewels secured respectivelyat the end of each pawl engaging said teeth.

7. The device of claim 6 wherein the edges of said jewel at the end ofsaid first pawl engage both the front and rear face of a tooth of saidgear.

8. The device of claim 7 wherein another edge of said jewel engages asurface of said pawl stop.

9. The device of claim 7 wherein the front and rear faces of the teethof said gear form an angle of

1. An electromechanical stepping device comprising a magnetic yokehaving a pair of opposite facing poles, a movable air core coilrotatably supported between said poles on a shaft having a longitudinalaxis between and parallel to the opposite faces of said poles, a pair ofreset springs secured at opposite ends of said shaft and connected tosaid coil to apply current thereto, both said springs being rotatablewith said coil and shaft and returning said coil to a reset position, atoothed gear mounted on a central axis, said gear axis being alignedwith and perpendicular to said coil shaft axis, and a first pawl mountedat one end of said shaft to rotatably engage separate successive teethof said gear upon each return movement of said coil after application ofa current pulse to rotate said coil, said gear being stepped by onetooth during each return movement of said coil.
 2. The device of claim 1including a pawl carrier rotatably mounted at one end of said shaftsecuring said first pawl thereon, and a pair of limit stop pins mountedunder each end of said carrier to limit rotatable movement of saidcarrier.
 3. The device of claim 2 including a second pawl secured at oneside of said yoke to successively engage another one of said teeth ofsaid gear each time said first pawl engages a tooth.
 4. The device ofclaim 3 including a pawl stop secured at the other side of said yoke tolimit movement of said first pawl.
 5. The device of claim 4 wherein saidfirst and second pawls are mounted at the ends of springs.
 6. The deviceof claim 5 including a pair of jewels secured respectively at the end ofeach pawl engaging said teeth.
 7. The device of claim 6 wherein theedges of said jewel at the end of said first pawl engage both the frontand rear face of a tooth of said gear.
 8. The device of claim 7 whereinanother edge of said jewel engages a surface of said pawl stop.
 9. Thedevice of claim 7 wherein the front and rear faces of the teeth of saidgear form an angle of 90*.